1. Field of the Invention
The present invention relates to sewerage systems and the purification of wastewater, and particularly to an apparatus and method for the elimination of bacteria and microorganisms from wastewater discharged from a septic tank system by irradiation of the wastewater with ultraviolet light.
2. Description of Related Art
Many homes in rural and outlying areas are not connected to municipal water systems and therefore rely on wells or water tanks for water supply and septic tank systems for waste disposal. The septic tank is a water tank buried in the ground for receiving waste from the plumbing system, and usually several hundred gallons of water. Solid material is usually liquified by bacterial action within twenty four hours, with sludge settling to the bottom of the tank and the effluent being discharged into a drainfield.
Groundwater contaminated by harmful bacteria and microorganisms may re-enter the food chain either directly in the water supply to homes and businesses, or through irrigation of crops, or through ingestion by animals raised for human consumption. In recent years public awareness of the deleterious effects of discharging untreated wastewater into the environment has resulted in both voluntary and government mandated efforts to treat wastewater effluent in order to remove harmful bacteria and microorganisms before discharging the water back into the environment. Municipal water systems now include wastewater treatment plants to provide a central location in which the wastewater may be germicidally treated before discharge.
A few systems for the treatment of wastewater from septic tanks have been developed. U.S. Pat. No. 5,738,781, issued Apr. 14, 1998 to T. Carlson, describes a septic tank system for recycling water having a septic tank divided into multiple chambers including a chamber containing granulated charcoal for removing odors and a chamber containing coarse and fine gravel for filtering particulate matter. U.S. Pat. No. 5,707,513, issued Jan. 13, 1998 to Jowett, et al., shows a septic tank wastewater treatment apparatus using polyurethane foam blocks as a filter medium to support aerobic biological treatment. U.S. Pat. No. 5,632,896, issued May 27, 1997 to Vandervelde, et al., teaches a filtration system using producing an ultra-thin film surface of water for more effective treatment by aerobic bacteria through a layer of fabric or sand.
U.S. Pat. No. 5,620,602, issued Apr. 15, 1997 to R. E. Stuth, discloses a device placed in a second chamber of a septic tank which froths the wastewater through a packing media having a high surface area to volume ratio to improve aerobic bacterial digestion of organic waste. U.S. Pat. Nos. 4,250,040 and 4,104,166, issued Feb. 10, 1981 and Aug. 1, 1978, respectively, to J. LaRaus, teach a method of treating septic tank wastewater by passing the waste through ozonating tanks which diffuse ozone through the water, at least one of the tanks having a charcoal filter, ozonating the wastewater being beneficial in promoting aerobic biodegradation of organic waste.
Chlorination has been used for the purification of water. However, many states and counties now forbid the discharge of chlorinated wastewater due to its adverse affects on vegetation. In any event, chlorination requires the use of tablets in the septic tank to chlorinate the water and then additional tablets to dechlorinate the water before discharge, an expensive, inconvenient process entailing the risk of chemical damage to the environment.
In the scheme of the present invention, the previously described water treatments involving filtration, aerobic digestion, ozonating and chlorinating are referred to as pretreatment methods. They are effective in liquefying wastewater, removing particulate matter, and removing between 70% and 85% of harmful microorganisms. The present invention utilizes irradiation with ultraviolet light (UV) to complete purification of the wastewater before discharge, particularly to eliminate E. coli and various forms of fecal coliform bacteria. Ultraviolet radiation offers several advantages. UV is effective against all microorganisms. It is economical, purifying hundreds of gallons per kilowatt hour. UV is safe, not requiring dangerous chemicals with the corresponding risk of overdose or danger to the environment. UV provides continuous germicidal action without special attention or measurement, and without leaving a chlorine taste in recycling systems and without corrosion problems affecting the plumbing.
It is known that irradiation of water with ultraviolet light within the range from about 150 nanometers through about 300 nanometers is effective in destroying microorganisms. The purification of fresh water by ultraviolet radiation for drinking purposes is described in U.S. Pat. No. 4,762,613, issued Aug. 9, 1988 to M. R. Snowball, for use in the laboratory in U.S. Pat. Nos. 4,276,256, issued Jun. 30, 1981 to N. A. Karamian and 4,296,328, issued Oct. 20, 1981 to M. D. Regan, and for aquarium or swimming pool use in U.S. Pat. No. 3,971,947, issued Jul. 27, 1976 to Lambert, et al. The use of racks of ultraviolet lamps in wastewater treatment plants is shown in U.S. Pat. No. 5,019,256, issued May 28, 1991 to Ifill, et al., U.S. Pat. No. 5,256,299, issued Oct. 26, 1993 to Wang, et al., U.S. Pat. No. 5,422,487, issued Jun. 6, 1995 to Sauska, et al., and U.S. Pat. No. 5,624,573, issued Apr. 29, 1997 to R. Wiesmann.
U.S. Pat. No. 4,700,101, issued Oct. 13, 1987 to Ellner, et al., teaches the construction of UV lamps which may be connected end to end or side by side. U.S. Pat. No. 4,728,368, issued Mar. 1, 1988 to E. A. Pedziwiatr, describes cleaning the quartz tubes housing ultraviolet lamps used in wastewater treatment by ultrasound. U.S. Pat. No. 5,144,146, issued Sep. 1, 1992 to A. Wekhof, teaches a method of treating waste water using pulsed UV radiation over a broad band at different power levels to cover the full range of microbial organisms. U.S. Pat. No. 5,208,461, issued May 4, 1993 to F. D. Tipton, discloses a wastewater treatment system including a stainless steel box having a lid, an inlet, an outlet, and a housing having a plurality of UV lamps disposed at an acute angle relative to effluent flow, the flow being substantially horizontal.
International Patent WO 84/03880, published Oct. 11, 1984, shows a water purification chamber which is cylindrical and oriented vertically with a UV lamp in the center of the cylinder, 5 vertical chambers arranged radially around the lamp, an inlet in the first chamber, an outlet in the fifth chamber, and communication between adjacent chambers alternating between top and bottom so that the water travels in a long path from the first chamber to the fifth chamber to ensure a sufficiently long exposure to UV radiation. European Patent No. EP 202,820, published Nov. 26, 1986, describes a water purifier with a UV lamp in a quartz tube enclosed in a jacket having inlet and outlet tubes on the side of the jacket, the jacket having helical grooves defined in its exterior causing a turbulent flow of the water to ensure all of the water comes close to the UV tube for effective germicidal action.
It is known that some western States in the continental United States are beginning to experiment with the installation of ultraviolet lamps for water purification in some septic tank systems. However, currently the lamps are being housed in concrete vaults, an expensive, time consuming, and inconvenient mode of installation. There is therefore a need for a simple, economical, easily serviceable, waterproof apparatus and method for installing an ultraviolet light water purification unit in a septic tank system.
A further known problem with ultraviolet water purification units arises from housing ultraviolet lamps in quartz tubes, which are used because quartz is essentially transparent to UV radiation at the wavelengths used in wastewater treatment, having a high transmittance and allowing the passage of UV radiation with little loss in power. However, particulate matter remaining in wastewater even after filtering and other pretreatment methods has a tendency to adhere to the quartz tube, diminishing the power of UV radiation emitted from the tube and requiring periodic cleaning and frequent maintenance. Quartz tubes are also fragile, requiring special precautions in handling and installation. It is therefore desirable to provide a housing for the ultraviolet lamp which resists contamination by particulate matter and which is more rugged and therefore able to withstand rough handling during installation and maintenance.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed.